The present invention relates to a chain stitch sewing machine and, more particularly, to an in-line chain stitch sewing machine having a thread trimmer system which operates automatically below the needle plate of a cylinder bed sewing machine.
The sewing machine of the present invention is used exclusively to form a chain stitch, which is well known in the art as a type 401 stitch, and is to be distinguished from machines forming other types of stitches such as, for example, a lock stitch formed by sewing machines disclosed in U.S. Pat. Nos. 4,401,046 and 4,365,568. The sewing machine of the present invention forms a chain stitch by using an in-line looper system which is distinguishable from a machine using a transverse looper system such as, for example, the machines disclosed in U.S. Pat. Nos. 4,726,305 and 4,834,010. A sewing machine using a transverse looper system forms the chain stitch by cycling through an elliptical path that is perpendicular to the direction of sewing. Because of the perpendicular relationship and ample space below the needle plate, trimmer systems cutting below the needle plate have been used on machines using the transverse looper system. The problem with using such machines, however, is that they are limited to about 5 needles and a small sewing width.
Machines using the in-line looper system, however, can use more than 30 needles and provide an unlimited sewing width. As such, they are more desirable for certain commercial applications. In such machines, however, the loopers move only in a straight line parallel to the direction of sewing and, as such, require the use of an extra component, a set of coaxially aligned spreaders, one for each needle, to form the stitch by moving perpendicular to the direction of sewing. Because of the extra components, one spreader for each needle, there is little space for positioning an automatic thread trimmer system below the needle plate. Instead, thread trimmers typically have been positioned above the needle plate congesting the working space above the needle plate, such as, for example, the machine disclosed in U.S. Pat. No. 4,461,229.
U.S. Pat. No. 4,879,960 issued to Prais discloses an in-line thread trimmer system that automatically cuts the threads below the needle plate. However, this thread trimmer system is adaptable for use with a flat bed sewing machine only and cannot be used with a cylinder bed sewing machine because of the smaller circumference of the cylinder bed. Generally, the flat bed type sewing machine is used for sewing in the horizontal plane over the surface of the bed, which means there is no restriction on the bed circumference. The smaller circumference of the cylinder bed type sewing machine allows goods such as waistbands or cuffs to encircle the bed and be sewn. Consequently, size considerations are of paramount concern with the cylinder bed sewing machine, making the addition of a thread trimmer system extremely difficult. As a result, thread trimmers have typically been positioned above the needle plate for cylinder bed sewing machines, congesting the working space above the needle plate.
A prior art chain stitch sewing machine having an in-line looper system is indicated generally at 10 in FIG. 1. Machine 10 comprises a base 12, having a bed plate 14 supported atone end and a vertical standard 16 supported at the other end, and a horizontal arm 18 extending from vertical standard 16 over bed plate 14 to support a head 20. A needle bar 22 is slidably mounted within head 20 and carries a needle holder 24 in which ten needles 25 are secured. The needles 25 descend from a top to a bottom position through oblong openings in a foot 28 supported by head 20 and a needle plate 29 supported on bed plate 14.
Continuing with FIG. 1, the sewing direction into machine 10 is indicated by an arrow 30 and the sewing direction out of machine 10 is indicated by an arrow 31. A U-shaped slide assembly 32 is mounted on base 12 and opens against the sewing direction toward arrow 30. A knife support bracket 36 is slidably mounted within assembly 32 and carries ten arrow-shaped knives 38 which move coaxially with the sewing direction between a retracted position as shown and an extended position in which bracket 36 is moved against the closed end of slider assembly 32. An L-shaped actuator arm 40 is pivotally connected to bed plate 14 by a screw 42 and has one end pivotally connected to bracket 36. As can be seen in FIG. 1, the prior art machine 10 has a relatively large bed circumference.
Accordingly, there is a need for an in-line thread trimmer system for use with a cylinder bed sewing machine, which thread trimmer system automatically cuts the threads below the needle plate and, more specifically, one that cuts the last chain stitch being sewn in a first piece of material so that it does not unravel and then positions the tail end of the threads so that they are automatically set up for the first chain stitch in the next piece of material to be sewn.